The present invention relates to a route information supply system, and in particular, to a server device supplying route information, a map display device communicating positional information and the route information with the server device, and a route information supply system supplying map information taking traffic information into consideration.
Conventional navigation systems installed in a mobile unit (vehicle, etc.) are equipped with a storage medium (CD-ROM, DVD-ROM, etc.) storing map information and provide route guidance to a driver, etc. by reading necessary map data from the storage medium. In recent years, communicating navigation systems are being proposed instead of such navigation systems, in which map information is prestored in a server device which is placed outside the mobile unit and a terminal device installed in the mobile unit obtains the map information by communicating with the server device and thereby provides route guidance.
Regarding such communicating navigation systems, techniques for acquiring a detailed map of a particular region (e.g. destination) from the server device as needed are well known. However, even if such a detailed map of the destination can be obtained, memory usage efficiency gets worse when the distance from the destination is long. To avoid the problem, techniques capable of acquiring detailed maps with proper timing have been proposed.
For example, in a technique disclosed in JP-A-11-38872, traffic information is collected and when the mobile unit approaches a construction site, a traffic jam, etc., a detailed map of the point of construction, traffic jam, etc. is acquired and a route which has already been set is altered using the detailed map.
As for the delivery of maps, a technique for reducing the mount of map data has been disclosed in JP-A-2001-84493, in which a map of a limited area (within a prescribed distance from the route or within a preset number of intersections from the route) is cut out and delivered, leaving out map information on distant areas which are not directly relevant to the route guidance, by which the amount of map data is reduced. According to the technique, in the case where a cut-out width for cutting out a zonal map along the route is designated by the distance, setting a large width causes an increase in the amount of map data (including map information not directly relevant to the route guidance). On the other hand, if the cut-out width is set small, relevant intersections might not be included in the map which is cut out. In the case where the cut-out width is designated as an area within a prescribed number of intersections from the route, the width of the zonal map changes sharply in areas having large variations in the interval between intersections, by which areas with no map might be displayed on the screen when the terminal is displaying an area in the vicinity of an intersection corresponding to a narrow width of the zonal map. To avoid displaying such areas with no map, it is possible to adjust the display scale depending on the width; however, the display scale after the adjustment might not suit the user's intention. Meanwhile, in a method being studied, maps are cut out gradually dropping their finenesses as the distance from the route increases. For example, information on an area nearby the route can be certainly notified to the driver while cutting down the amount of map data, by partitioning an area for a route vicinity map into a plurality of areas based on the distance from the route, generating the route vicinity map by cutting out maps of areas in the vicinity of the route as detailed maps while cutting out maps of areas distant from the route as extensive maps, and delivering the generated route vicinity map.
However, in the above technique, even if traffic information is gathered and delivered to the mobile unit together with the map, the information is not used until the mobile unit approaches a construction site, traffic jam, etc. Therefore, even when a construction site, traffic jam, etc. exists on the route or nearby the route, the fact is not previously known at the stage of the route search, by which options for avoiding the traffic jam, etc. are necessitated to be limited.
Further, when the map delivered is displayed, the way of processing map elements existing on a boundary line between map areas having different finenesses becomes a problem. Specifically, if such map elements are partitioned at the boundary line into configurations having different finenesses, problems like unconformity of road joining points, discontinuity of background configurations, redundancy of name display, etc. are caused. Such reduction of the information amount by changing the fineness of map areas distant from the route can surely decrease the amount of map data; however, the aforementioned irregularities of configuration occurs to the map elements existing on the area boundary and thereby visibility of the map is deteriorated.
It is therefore the primary object of the present invention to realize map display taking traffic information into consideration in the route search carried out by a communicating route information supply system.
Another object of the present invention is to provide a map display system capable of maintaining visibility of map display even when the amount of data of the route vicinity map is reduced.